#include <crt_util.h>

#define BASE64_PAD     '='
#define BASE64DE_FIRST '+'
#define BASE64DE_LAST  'z'

static const char base64en[] = {
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
    'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
    's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',
};

/* ASCII order for BASE 64 decode, -1 in unused character */
static const signed char base64de[] = {
    /* '+', ',', '-', '.', '/', '0', '1', '2', */
    62,
    -1,
    -1,
    -1,
    63,
    52,
    53,
    54,

    /* '3', '4', '5', '6', '7', '8', '9', ':', */
    55,
    56,
    57,
    58,
    59,
    60,
    61,
    -1,

    /* ';', '<', '=', '>', '?', '@', 'A', 'B', */
    -1,
    -1,
    -1,
    -1,
    -1,
    -1,
    0,
    1,

    /* 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', */
    2,
    3,
    4,
    5,
    6,
    7,
    8,
    9,

    /* 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', */
    10,
    11,
    12,
    13,
    14,
    15,
    16,
    17,

    /* 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', */
    18,
    19,
    20,
    21,
    22,
    23,
    24,
    25,

    /* '[', '\', ']', '^', '_', '`', 'a', 'b', */
    -1,
    -1,
    -1,
    -1,
    -1,
    -1,
    26,
    27,

    /* 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', */
    28,
    29,
    30,
    31,
    32,
    33,
    34,
    35,

    /* 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', */
    36,
    37,
    38,
    39,
    40,
    41,
    42,
    43,

    /* 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', */
    44,
    45,
    46,
    47,
    48,
    49,
    50,
    51,
};

int base64_encode(const unsigned char* in, unsigned int inlen, char* out)
{
    unsigned int i, j;

    for (i = j = 0; i < inlen; i++) {
        int s = i % 3;

        switch (s) {
        case 0:
            out[j++] = base64en[(in[i] >> 2) & 0x3F];
            continue;
        case 1:
            out[j++] = base64en[((in[i - 1] & 0x3) << 4) + ((in[i] >> 4) & 0xF)];
            continue;
        case 2:
            out[j++] = base64en[((in[i - 1] & 0xF) << 2) + ((in[i] >> 6) & 0x3)];
            out[j++] = base64en[in[i] & 0x3F];
        }
    }

    /* move back */
    i -= 1;

    /* check the last and add padding */
    if ((i % 3) == 0) {
        out[j++] = base64en[(in[i] & 0x3) << 4];
        out[j++] = BASE64_PAD;
        out[j++] = BASE64_PAD;
    } else if ((i % 3) == 1) {
        out[j++] = base64en[(in[i] & 0xF) << 2];
        out[j++] = BASE64_PAD;
    }

    return BASE64_OK;
}

int base64_decode(const char* in, unsigned int inlen, unsigned char* out)
{
    unsigned int i, j;

    for (i = j = 0; i < inlen; i++) {
        int c;
        int s = i % 4;

        if (in[i] == '=')
            return BASE64_OK;

        if (in[i] < BASE64DE_FIRST || in[i] > BASE64DE_LAST || (c = base64de[in[i] - BASE64DE_FIRST]) == -1)
            return BASE64_INVALID;

        switch (s) {
        case 0:
            out[j] = ((unsigned int)c << 2) & 0xFF;
            continue;
        case 1:
            out[j++] += ((unsigned int)c >> 4) & 0x3;

            /* if not last char with padding */
            if (i < (inlen - 3) || in[inlen - 2] != '=')
                out[j] = ((unsigned int)c & 0xF) << 4;
            continue;
        case 2:
            out[j++] += ((unsigned int)c >> 2) & 0xF;

            /* if not last char with padding */
            if (i < (inlen - 2) || in[inlen - 1] != '=')
                out[j] = ((unsigned int)c & 0x3) << 6;
            continue;
        case 3:
            out[j++] += (unsigned char)c;
        }
    }

    return BASE64_OK;
}
